264 A SHORT HISTORY OF SCIENCE 



in England. In addition, Hales made important studies on the 

 atmosphere, and invented the manometer, which he applied to the 

 measurement of the arterial blood pressure in the horse, and the 

 upward root pressure in plants, besides accomplishing much other 

 good work. Hales will perhaps be longest remembered in chem- 

 istry for his skilful use of the pneumatic trough, a simple but in- 

 dispensable laboratory appliance for the easy collection of gases 

 in a closed vessel over water, and especially for his studies on air. 



MEDICAL SCIENCE AND MEDICAL THEORY IN THE SEVENTEENTH 

 CENTURY. THOMAS SYDENHAM. In the middle of the seven- 

 teenth century medical theory took a long step forward under 

 the influence of Thomas Sydenham (1624-1689), often called "the 

 English Hippocrates" because of the naturalism and rationalism 

 which he urged in medicine and because of the sanity of his opinions 

 and theories. Setting aside magic, mysticism, and the medical 

 chemistry of Paracelsus, and insisting on a material basis (materies 

 morbi) for the causes of disease, Sydenham laid the foundations 

 of modern scientific medical philosophy and practice. He was a 

 close friend of Locke, the philosopher, by whose materialistic 

 and rationalistic ideas he was doubtless influenced, and was 

 also a correspondent of Boyle. His famous definition of disease 

 as, " An effort of nature, striving with all her might to restore the 

 patient by the elimination of morbific matter," is still interesting 

 for its implication of the modern idea of disease as a struggle for 

 existence between pathogenic matters (such as microbes) and the 

 inner forces of the body. 



It is, however, to Vesalius and Harvey, to Leeuwenhoek and 

 Kircher and Malpighi and the other microscopists of the seven- 

 teenth century, and their successors, i.e. to the experimenters and 

 laboratory workers, rather than to Sydenham or his successors, 

 that medical science is chiefly indebted, since no great progress 

 could be made in sound medical theory or rational medical prac- 

 tice until anatomy, physiology and microscopy had paved the 

 way for a more scientific pathology. 



THE BEGINNING OF MODERN IDEAS OP LIGHT AND OPTICS. 

 The nature of light, darkness and vision are very old problems. 



